Spinal muscular atrophy (SMA)

Spinal muscular atrophy is a rare inherited condition in which the motor neurones of the spinal cord die off — the cells that carry the instruction to contract from the nervous system to the muscles. The muscles themselves are healthy, but the instruction never arrives, and they weaken. With this condition it particularly matters to read something recent: over the past few years treatments have appeared that change how the disease runs, and a great deal of older writing is out of date. From that follows the practical rule of this page — in SMA time works against the person, and the earlier the diagnosis is made and treatment started, the more movement is preserved. Below: how the condition is recognised at different ages, why delay is costly, and what matters most in day-to-day care.

What happens in SMA

The motor neurones sit in the front horns of the spinal cord. To survive they need a protein called SMN, produced from the SMN1 gene. In SMA that gene is altered or missing, there is not enough of the protein, and the neurones gradually die. The muscles closest to the trunk are affected first: shoulders, hips, back, and the muscles used for breathing and swallowing.

Alongside it sits a "backup" gene, SMN2, which makes a small amount of the same protein. People carry different numbers of copies of it, and that is one reason why the same diagnosis can run so differently — from a severe form in a baby to slowly increasing weakness in an adult.

SMA is inherited in a recessive pattern. Carriers are usually entirely healthy people who know nothing about it, and carrying the altered gene is considerably more common than most people assume. If both parents are carriers, then for each pregnancy there is roughly a one in four chance the child will have SMA, two in four that the child will be a carrier without the condition, and one in four that they will be neither. Some rarer forms are inherited differently, and a few are not passed on at all.

One thing worth saying at once: SMA does not affect intelligence. The weakness concerns muscles, not thinking, speech or the ability to learn. Children with SMA attend mainstream school and often do markedly better than their classmates wherever brains and patience are what count.

What it looks like in a baby

In the youngest children the picture is recognised not from one sign but from a combination. What should prompt concern:

• the baby feels floppy when picked up, and lies with the legs splayed out flat;
• arms and legs move weakly while the face is expressive and the gaze alert — a very characteristic combination;
• poor head control, not rolling over or sitting on time, or losing skills already gained;
• a weak, quiet cry and a feeble cough;
• difficulty sucking, tiring during feeds, choking, poor weight gain;
• breathing mainly with the tummy, the chest seeming to sink in on each breath while the abdomen pushes out;
• sometimes fine flickering movements of the tongue.

One common confusion is worth clearing up: muscle twitching and a fine tremor of the fingers are not seizures or fits. SMA does not cause epileptic seizures, and the two should not be mixed up.

If you see this combination in a baby, do not wait for the next routine check. Tell the doctor plainly that muscle weakness is what worries you, and ask for that to be assessed. The diagnosis is confirmed by an ordinary blood sample sent for genetic testing, and the result comes back quickly — this is not an investigation that drags on for months.

What it looks like in an older child and in an adult

The later the condition begins, the milder it usually runs, and the less obvious the first signs are — they are easily put down to clumsiness or laziness. In a child who is already walking, what stands out is:

• difficulty getting up from the floor: the child turns over, pushes their hands against their knees and effectively climbs up their own legs;
• stairs are hard work, with both hands on the banister or both feet placed on each step;
• a waddling walk, frequent falls, trouble running and jumping;
• weakening shoulders — struggling to lift the arms, put on a rucksack or hang from a bar;
• a curve developing in the spine;
• a fine tremor of the fingers with the arms held out.

In adults the condition can begin with weakness in the hips and shoulders that builds over years: getting out of a chair or a low car, or walking uphill, becomes hard. Such weakness is often blamed on age or extra weight for a long time, and genetic testing puts the matter straight. The point of early diagnosis in adults is the same as in children: to hold on to what still works.

Why timing decides so much here

This is the central idea of the whole page. A motor neurone that has died does not come back. Treatment can stop or sharply slow the loss of further cells, but it cannot restore the ones already gone. The consequence is simple: the outcome depends not only on which treatment is given but on when it is started. A child treated before noticeable weakness appears may develop along an almost ordinary path; the same child a few months later presents a different picture.

This is why many countries have added SMA to newborn screening — the heel-prick blood test done in the first days of life. Its purpose is to find the condition before the first symptoms and start treatment while there is nothing yet to lose. Screening programmes differ between countries and continue to expand, so it is worth checking whether SMA is included where you live.

Other things that come down to timing:

• the confirmatory test is quick; if a doctor suspects SMA, there is no need to queue through a long chain of other investigations first;
• if someone in the family already has SMA, carrier testing and genetic counselling belong before a pregnancy, not during it;
• if weakness together with breathing or swallowing difficulty has appeared and is increasing, that is a reason to seek help now rather than to watch and wait.

What can now change the course of the condition

Until recently all that could be offered in SMA was support. There are now medicines that act on the cause — the shortage of SMN protein. They fall into three classes:

• medicines that alter how the backup SMN2 gene works so that it produces the full protein; these are given into the spinal fluid;
• medicines with the same purpose, taken by mouth as a liquid, every day;
• gene replacement therapy — a single infusion delivering a working copy of the gene using a viral vector.

Brand names are deliberately left out here: the choice depends on age, weight, the form of the condition, how much function is preserved, the results of genetic testing and what is available in a given country. The decision is made by a specialist neuromuscular centre, which then follows the person up and measures the effect on motor function scales. These medicines have side effects and monitoring requirements, so they are a subject for an appointment rather than for online descriptions.

Something worth keeping in mind: medicine does not replace everything else. Physiotherapy, respiratory support, nutrition and orthopaedic care are all still needed, and it is the combination that produces results. And research continues and protocols change, so information that is two or three years old is worth checking again.

Breathing — where the main risk lies

If only one thing about care is remembered, let it be breathing. It is not only the arms and legs that weaken but the muscles between the ribs and those that produce a cough. Secretions cannot be cleared, and an ordinary cold in such a child behaves quite unlike a cold in anyone else: within a day it can turn into a serious chest infection.

So with a respiratory infection you seek help early rather than waiting it out. Ring the doctor on the day it starts, and do not wait to see whether it clears by itself. Call an ambulance or take the child to hospital immediately if any of these appear:

• fast, shallow or visibly laboured breathing, with the skin drawing in between the ribs and above the collarbones;
• blueness or pallor of the lips or fingertips;
• the child cannot cough anything up, and breathing sounds rattly;
• unusual sleepiness, lethargy or confusion;
• refusing food and drink, with signs of dehydration;
• pauses in breathing during sleep, loud snoring with gaps, morning headache in an older child or adult — these point to inadequate breathing overnight.

In Spain, Italy, Portugal, Poland and Ukraine the single European emergency number 112 is in use. It helps to draw up a written plan with the treating centre in advance: what to do in the first hours, which equipment to use at home, which hospital to go to and who to call. Keep it printed and take it with you.

What helps prevent trouble: airway clearance techniques and devices that assist coughing and, where needed, non-invasive breathing support through a mask, most often overnight. Flu and pneumococcal vaccination are recommended both for the person with SMA and for everyone living with them; ask the doctor about protecting infants against other respiratory infections, as programmes differ between countries.

Swallowing and feeding

Swallowing sits right next to breathing, because food that goes the wrong way ends in the same pneumonia. Feeds that drag on, choking, coughing during meals and weight loss are all reasons to see a swallowing specialist and a dietitian without delay. Sometimes the texture of food is changed, sometimes a feeding tube or a gastrostomy is placed. That is not a defeat or a "final step": feeding through a gastrostomy often restores energy, removes the fear of choking and turns mealtimes back into something calm rather than a ninety-minute ordeal. Long gaps without food are poorly tolerated in SMA, so nutrition and fluids need particular attention during any illness.

Movement, the spine and everyday life

The rest of the care is aimed at keeping the body serviceable and comfortable for as long as possible.

• Physiotherapy and stretching, regularly and in small amounts: they keep joints from stiffening and preserve range of movement.
• Orthoses, splints and standing frames help with posture, take load off joints and are good for the bones.
• A wheelchair, including a powered one, is not a sign of decline but a way of regaining independence and saving energy for what matters more.
• The spine is watched from the start: with weak muscles a curve increases and interferes with breathing. Bracing is used, and where scoliosis is marked, surgery is discussed.
• The hips and bone strength are checked: with little weight-bearing the bones weaken, and fractures happen after minor knocks.
• An occupational therapist finds the aids that give back simple things: holding a spoon, using a phone and a computer, driving a wheelchair independently.

And a general point. People with SMA study, work, drive adapted cars and raise children. Support here exists to remove obstacles, not to express pity. Conversations about equipment are better started early rather than at the point where nothing works without it: that way it is easier to choose and to get used to calmly.

Online consultation

A remote appointment is a good first step when all you have is a worry: describing exactly what you notice in your child or in yourself, and working out whether genetic testing is needed and which specialist to see. The doctor can help you frame the question for a face-to-face appointment so that the weakness is not put down to temperament or age. For those already diagnosed, a consultation helps in going through a report, preparing questions for the neuromuscular centre, and discussing the plan for a cold, nutrition, the physiotherapy routine, carrier status and family planning. Signs of respiratory failure are not assessed remotely — those mean hospital straight away.

This material is for information only and does not replace medical advice.